Rechargeable batteries such as batteries made up of many lithium-ion cells can be used in many applications, including for example, electric propulsion vehicle (“EV”) and hybrid electric vehicle (“HEV”) applications. These applications often require advanced battery systems that have high energy storage capacity and can generate large amounts of heat that needs to be dissipated. Battery thermal management of these types of systems generally requires that the maximum temperature of the individual cells be below a predetermined, specified temperature.
Cold plate heat exchangers are heat exchangers upon which a stack of adjacent battery cells or battery cell containers housing one or more battery cells are arranged for cooling and/or regulating the temperature of a battery unit. The individual battery cells or battery cell containers are arranged in face-to-face contact with each other to form the stack, the stack of battery cells or battery cell containers being arranged on top of a cold plate heat exchanger such that an end face or end surface of each battery cell or battery cell container is in surface-to-surface contact with a surface of the heat exchanger.
Heat exchangers for cooling and/or regulating the temperature of a battery unit can also be arranged in between the individual battery cells or battery cell containers that form the stack or battery unit, the individual heat exchangers being interconnected by common inlet and outlet manifolds. Heat exchangers that are arranged or “sandwiched” between the adjacent battery cells or battery cell containers in the stack may sometimes be referred to as inter-cell elements (e.g. “ICE” plate heat exchangers) or cooling fins.
Temperature uniformity across the surface of an individual battery cell as well as the temperature uniformity of all the cells in the battery pack is of significant importance since the battery is a chemical reaction of which its performance is significantly affected by the temperature at which it runs. A thermal gradient in the battery will cause some cells to charge and discharge faster than others, causing battery pack durability issues. Accordingly, temperature uniformity across the surface of the heat exchanger is an important consideration in the thermal management of battery units since temperature uniformity across the surface of the heat exchanger helps to ensure that the temperature differential between individual battery cells in the overall battery unit is kept to a minimum. It is generally understood that the temperature of the coolant travelling through the heat exchanger will increase as it travels through along the length of the fluid channel(s) from the inlet to the outlet. Given that the surface temperature of the heat exchanger will generally be proportional to the temperature of the coolant or fluid travelling through the heat exchanger, the temperature of the coolant will be colder at the inlet end of the heat exchanger and warmer near the outlet end of the heat exchanger resulting in an inherent temperature differential across the surface of the heat exchanger. Accordingly, battery cells arranged proximal to the inlet end of the heat exchanger will be subject to a lower coolant temperature than battery cells arranged proximal to the outlet end of the heat exchanger resulting in a potential temperature differential between the individual battery cells, which generally is undesirable. Therefore, heat exchangers that offer improved temperature uniformity across the heat exchange surface may offer improved or more consistent cooling to the individual battery cells or battery cell containers across the entire surface of the heat exchanger plates.